Method of making a nitrate-phosphate fertilizer



United States Patent Alfred M. Thomson, 265 Buckingham Way, Apt. 402,San Francisco 27, Calif. Continuation of application er. N 35,783, lune13, 1969. This application Sept. 19, 1962, Ser. No. 224,618 1 Claim.(Cl. 7139) This application is a continuation of an earlier applicationhaving the same title and the Ser. No. 35,783, filed on the 13th day ofJune 1960, now abandoned. It is the aim and object of the presentapplication to present the same disclosure as that of the earlierapplication but with such changes in the language employed thatparticular emphasis is placed upon the novelties that I have introduced,thus solving the difiiculties on which previous attempts to build asatisfactory process have so far universally failed. For this reason Iwill first review briefly such failures and show why they wereforedoomed to failure. I will commence with a statement, also made inthe previous application, that in so far as chemical reactions areconcerned I am introducing nothing new. The novelty resides not in anyof such reactions, nor in the combination of same, but rather in the wayin which i have altered and deviated former attempts so as to form aprocess that is economically feasible and fully operative. When pastattempts are analyzed it is obvious that the use of the electric arc, ofexceptionally high temperatures produced by the combustion of fuel, ofheat recuperation to increase the economy of such use of fuel, ofshockcooling to preserve nitric oxide, etc, are all very old items inthe fixation of nitrogen. Nevertheless, the ultimate results ofvirtually any combination of such items has always ended in failure soit is not in the combination, per se, but HOW the combination isefiected that becomes the important item.

It is assumed that the reviewer is familiar with the various processesfor nitrogen fixation as thus referred to. Were it otherwise nospecification could possibly be understood. It would require literallyvolumes of technical literature to cover the subject and only thebriefest abstracts can be given. However, to one familiar with thesubject, applicants descriptions will be found both clear and lucid.

The are processes, known as Birkeland-Eyde, Schoenherr, lauling, etc.were technically a perfect success in so far as producing nitric oxideis concerned. For a time they were important, and in conjunction withvery cheap water power they produced notable amounts of nitrates. Butwhen the present cheap synthetic ammonia appeared they became obsolete.My use of the arc is thus manifestly distinct and dififerent from allthe old techniques in which the arc was the sole source of heat. Bydeforming said arc into sorn type of a flaming arc the nitric oxideformed was subjected to a type of shock-cooling in merely escaping fromsaid arc into the relatively cool circumambient air current which was aninescapable condition for satisfactory formation of said arc. Thesalient fault of the process was the extremely small yield of nitricoxide when compared with the current input, the literature indicating anefficiency of only about 3%. The arc was, of course, the sole source ofheat.

inasmuch as most of the energy produced today is based on fuel it isobvious that if the rise in temperature can be produced by the directcombustion of fuel such heat input will cost far less than any possiblearc-heating technique. This was originally introduced as early as theturn of the century in the so-called explosion technique of the Germaninvestigators who exploded coke-oven gas mixed with air in a type ofbomb and then released the resultant pressure almost instantaneously,producing a type of limited shock-cooling due to the expansion of theimprisoned gases. While the literature on the subject is extensive ithas shared the same fate as the arc processes previously referred to.

More recently this phase of nitrogen fixation was taken up under theauspices of our government by introducing a highly developed form ofheat recuperation to diminish the fuel consumption and simultaneously toachieve a form of so-called shock-cooling, the device used in both casesbeing a pebble bed heat-accumulator, alternately heated and cooled bythe reversal of flow of traversing gases. Like all others it failed,though only after the expenditure of much money, through threedifficulties. inasmuch as the formation of nitric oxide is endothermic,it is mandatory to heat the gases initially to a temperature well abovethe mandatory 4200 F., which introduces the first difficulty. It is verydif icult to reach the latter temperature consistently, let alone exceedit. The second is to preserve intact the walls of the heat accumulatorsthat soon become fissured and thus let gases byy-pass the pebble-packedinteriors. The third is due to an actual volatility of the refractoryused in both Walls and packing. heoretically, there is quite a marginbetween the temperature of fusion and of volatilization of therefractory selected, and the temperature of operation; but this vanishesin operation in View of the law of partial pressures when the enormousvolumes of the traversing gases is taken into consideration. The factremains that unavoidable spalling or" the pebbles is complicated by theactual deposition of volatilized MgO in the spaces between the pebbles.The over-all result was failure.

My method of overcoming all the difilculties enumerated in the precedingdescriptions is as follows: I do indeed use heat recuperation but NOT atthe temperatures used by others. I do use shock-cooling but not bypassing nitrous gases through a hot pebble bed, conti'ariwise, Icommingle the hot gases issuing from the heating stage with cold air insuch an amount that the mixed gases drop to the comfortableapproximation to 2800 P. which presents none of the aforementioneddifficulties when subjected to heat recuperation. In such comminglingthere is no actual loss of heat but merely a decrease in intensity, ortemperature, compensation for such loss in intensity being found in theincrease of mass involved. While the approximation, 2800 F., does notrender nitric oxide stable it makes further loss sufiiciently slow sothat the heat accumulators will speedily produce complete safety.

It will be obvious that in thus solving the difficulties attending heatrecuperation at high temperatures 1 have introduced another. it isimpossible to re-introduce all of the air required to cool the heataccua ulators into the actual heat cycle of nitrogen fixation. Assuminga top temperature of 4200 F. it will take about 50% by volume of coldair, both reduced to NTP, to produce 2800 F. in the mixture. Now incooling these accumulators, by reversal of how, this will yield moreheated air than can be re-introduced as before mentioned and some usemust be found for this heat discard outside of nitrogen fixation. Itwill also be obvious that the ENTIRE heat value of the fuel consumedwill be salvaged in this manner, thus adding immeasurably to theeconomics of the operation.

I now come to the use I make of arc-heating. It is used, substantially,only to supply the heat increment needed to sustain the 4200" F.temperature during the formation of nitric oxide thus making itunnecessary to temporarily increase combustion heat above thatintensity. Such consumption of electrical energy is quite small.Assuming that the gas leaving the arc contains about 2% of nitric oxidethis w'll involve only /2 kw. hr. per pound of fixed nitrogen. It willbe obvious that with such a low input of electrical energy and thesalvage, as highly a in situ.

made from the weak nitric oxide 'by suitable means as a heated air, ofsubstantially ALL'the fuel burned, the cost of nitrogen fixation can bemade very low 'mdeed.

So far I have dwelt only on nitrogen fixation and said nothing aboutphosphate, but to render-the dilute nitric acid transportable ormarketable somethting must be done, Itis true that full strength nitricacid can be that is done every day in malring ammonia the intermedi atebetween atmospheric nitrogen and nitric acid. But a glance at any pricelist will also show that relatively weak nitric acid is far cheaper, perpound of actual HNO contained, than the stronger acids. For this reasonI have 7 incorporated the decomposition of tri-calcium phosphate bymeans of nitric acid as a preferred way to use said acid. Itis true, andI am well aware, that there is nothing new in this application so far asthe chemical reactions are concerned but as an additive step in a longprocess claim it is certainly new as such a process as I shall nowdescribe is found nowhere.

It is obvious that the reaction between the dilute nitric acid producedfrom the air and rock phosphate will yield a mixture of calcium nitrateand either mono-calciurn phosphate, or di-calcium phosphate, or evenphosphoric acid. That is entirely under'the control of the operator asit resides in the relative proportions of acid, and phosphate which saidoperator sees fit to employ. Inasmuch as all three of these phosphoricacid combinations are acceptable to the plant I have usedthe expressionplantimmediately below the combustion chamber, are represented in thedischarging phase, cold air entering at the bottom and air atapproximately 2860 P. leaving at the top. Such a portion as can be usedin the combustion chamber is seen going in this direction, the remainderforming the Heat Discard previously referredto. In

' the event that the ratio between hot arc chamber discharge and coldair be as previously mentioned then about two-thirds of the heated airleaving the heat ac cumulators will pass'to the combustion chamber, theremaining one-third forming the discard. A simple calculation will showthat the Btu. content of said air will be practically equivalent to thatfurnished by the'fuel, thus rendering it possible to recoup almost theentire value of the fuel if said air be used in any other industry.Such:

utilization, while obvious, isnot considered a part of this disclosure,though it is of the utmost economic importance.

Attention will now be tocused'upon the cooled gas with its content ofnitric oxide which was discharged from the left hand pair of heataccumulators. I have shown this gas as entering a scrubber which may beof any conventional type suitable to the re-circulation of a slurry. The

slurry is composed'of water and finely ground rockphosphate, tri-calciumphosphate, and their decomposition assimilable-phosphorus compounds asageneric term for approximately 2800 F. by heat recuperation, is'rnixed'with sufficient fuel to raise the temperature to approximately'42fi0 F.after which the products of combustion pass into the arc-chamberrepresented just above the combustion chamber. Of course, there is anincipient formation of nitric oxide in these gases but unless somethingis done to prevent the resultant cooling action, due to the endothermiccharacter of said reaction, there will be a notable decrease in theformation of nitric oxide. For this reason I use the arc to the extentnecessary'to prevent such a drop in temperature and I have representedthe needed energy as Current entering the arc chamber. The overallresult is, therefore, that gases with approximately 2% of NO leave thearc'chamber at substantially 4200? F. and enter the shock-cooler,represented at the upper left hand corner. The three devices so far'referred to are merely empty chambers fit for the high temperaturesemploying and without any packing whatsoever. They are meant for thethorough mixing of the traversing gases that'the inherent reactions maytake place,

' and for substantially no other purpose.

In the shock-cooler I have indicated the admixture of an admixture be inthe ratio of 1 part of'cold air with 2 parts of hot. gas, by weight,then the resultant mixture instantaneously as possible so the air willenter through a thehot gases from the arc chamber with cold air. If such7 plurality of small'jets and create violent turbulence withinsaid'chamber. In this manner there will be butslight decomposition ofthe resident nitric oxide. 7

The next devices indicated, in the line below the combustion chamber,are four heat accumulators. The two immediately below the shock-coolerare represented in the charging phase, thus storing the heat abstractedfrom'the traversing gas, and the d'raw'ingshows cooled gas is-= suingfrom both. ,The righthand set of heatlaccumulators,

. mingling in a state of violent turbulence with cold air in. 7 theamount of 50% by weight of the hot gases, thus cans-- products, and,of'course, the calcium nitrate formed.

No mention has been made of the need of oxidation to convert the nitricoxide to nitric acid, but that is the inevitable outcome of thescrubbing' operation in view' of the large excess of free'oxygen stillremaining in the gas that has passed through both combustion and arcchamber; In spite of the conversion of a part ofthe entering oxygen intocompounds with carbon, hydrogen,

and'nitrogen, there will still be a large excessof uncon-' sumed oxygen.To this is now added the cold air in the shock cooler so it is evidentthat there will be no lack of oxygen in the gas involved in thescrubbing operation. As a corollary, it will be equally obvious that ifno tri calcium phosphate be added then the final product will be someform of dilute nitric acid dependent essentially on the amount of watertolerated in the scrubbing medium. l Inasmuch as all such material ispurely conventional there is no need for any fuller explanation. e

As represented in the drawing, however, rock phosphate is in use and theresultant slurry is shown as entering a drier for dehydration in orderthat it may be put in a marketable condition. It is obvious that anyuncombined nitric acid passing to the drier will at the higher temperaature and increased time have'ample opportunity to finish.

any reaction uncompleted in the scrubbing operation. Anitrogen-phosphate fertilizer is thus obtained and the ratio betweennitrogen and P 9 can obviously'be varied within wide limits by theoperator if he so desires, it being only necessary to increaseordecrease the amount of powdered rock phosphate added to the scrubbingmedium. 7 7

Having thus fully described my process and called attention to thespecific ditferences between my process and the many previous attemptsat the direct fixationof ing sufficient fuel therein until .atemperature of approxi-' mately 4200 F. is obtainedymaintainingsaidtempera ture by the use of the electric arc during sustained for mation'of nitric oxide until substantial equilibrium has been obtained;shock-cooling the resultant gases by coming'a substantiallyinstantaneous drop in temperaturejto yapproximately 2800 F.,thusobtaining substantial stability ofthe resident nitric oxide andavoiding all ditliculties in subsequent heat recuperation; storing theheat f i still remaining in said gases in heat accumulators; subsefquently transferring said heat to incoming, traversing air which thusbecomes heated to approximately 2300" F.; dividing said air, heated byheat recuperation, into two portions representing approximatelyone-third and twothirds respectively; re-cycling the larger portion tothe combustion step previously prescribed and discarding the smallerportion from the nitrogen fixation cycle for use elsewhere, said discardrepresenting substantially the heat equivalent of the fuel consumed inthe combustion step; scrubbing the nitric oxide containing gases thatwere previously cooled by passage through heat accumulators with aslurry consisting of a Water suspension of finely divided tri-calciumphosphate to produce a mixture of calcium nitrate and plant assimilablephosphates; continuously recycling a portion or" said slurry and dryingthe remainder to form a nitrate-phosphate fertilizer.

References Qited in the file of this patent UNITED STATES PATENTSPauling Dec. 13, 1904 Pauling Mar. 13, 1906 Saarbach Aug. 27, 1912Bundick Apr. 19, 1932 Johnson Sept. 6, 1932 Hechenbleikner June 4, 1935Pike June 30, 1953 Daniels Oct. 27, 1953 FOREIGN PATENTS Great Britain1907

